So with real image pixels, multiple pixel fires are trigged by 301s, since its actually really just an img tag and thats the only way to fire multiple ones (ie. network a's, network b's, your's).
Usually you have a few options. You can set two pixels at the network (if supported), you can use an iframe at the network with both pixels (if supported), you can hack the pixel fire code to do do a redirect to the other pixel or itself again under certain circumstances. If you can use postbacks instead, you can do some cURL requests on the two postback URLs, etc.
And I haven't played with the advanced pixel but it probably tackles this too.
You can also pay me $30 and I'll get this done for you fast.